When are humans most happy? To answer this question, researcher Matt Killingsworth built an app, Track Your Happiness, that let people report their feelings in real time. Among the results: We're often happiest when we're lost in the moment.

He's now a Robert Wood Johnson Health and Society Scholar examining such topics as the relationship between happiness and the content of everyday experiences, the percentage of everyday experiences that are intrinsically valuable, and the degree of congruence between the causes of momentary happiness and of one's overall satisfaction with life.

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GUY RAZ, HOST:

It's the TED Radio Hour from NPR. I'm Guy Raz. And on the show today, the one thing we can pretty much all agree we want - happiness.

DAN GILBERT: Well, of course.

RAZ: This is Dan Gilbert, happiness expert.

GILBERT: If you write a book with the word happiness in the title, you get one question over and over.

RAZ: And the question he gets?

GILBERT: Hey, Doc, what's the secret of happiness?

RAZ: Yeah. So what is it?

GILBERT: Well, the first thing is rather than answering the question, let's just think about it for a moment. Is there really a possibility, A, that it's a secret and only I know it and you don't, and, B, that it's a secret at all?

RAZ: Sadly, this is true because if there is one thing we learned from working on today's show it's that there is no secret to happiness. But there are plenty of ideas about it, all of which we'll explore this hour - ideas from science, design, philosophy. And the thing is, a lot of these ideas are surprisingly simple.

GILBERT: But, you know, when people ask about secret of happiness and you tell them, well, take more time in your social relationships, worry less about things and more about experiences, they kind of nod and look at you and say, yeah, but what about the secret? Because the secret of happiness is like the secret of dieting, there's no secret.

(PHONE RINGING)

RAZ: Pharrell, are you there?

PHARRELL WILLIAMS: Yes, sir.

RAZ: So this is your song, man. I mean, "Happy" - this is climbing the charts around the world. So I'm thinking, like, you must have the secret.

WILLIAMS: OK.

RAZ: I mean, no, seriously.

WILLIAMS: Well, you know what? Look, look. I'm not a guy that's walking around and smiling every day. I have - we all have our ups and downs and our lefts and our rights and our diagonal, you know. But really, you know, a much more simple way to look at it is to remember that you deserve to be happy. It's a natural born right.

RAZ: Fair enough. All right. Pharrell, we're going to listen to the rest of the show, and I will meet you on the other side. OK?

WILLIAMS: Yes, sir.

(SOUNDBITE OF SONG, "HAPPY")

RAZ: And by the way, you have to check out the video to this song. It will literally make you happy. Transcript provided by NPR, Copyright NPR.